I'm suprised this thread has not talked more about Dave Brown's Southern Sorghum. I've used it for years with no problems at all. Being a contact cement, you do only get one chance, but by making the skins a little overlarge, I've never had a major mistake. Using waxed paper between the core and skins helps too. It works great, is lighter than epoxy and you can keep building in 30-40 minutes. The only thing I do is mix a little blue latex paint in it - a couple of drops - to color it so you can see better where it's spread. The expanding aspect of the polyurethane glue worries me - but there are several methods, inlcuding epoxy, which obviously work. I've never had a delam problem in the hot sun, but your mileage may vary. On a project, I'll usually use Sorghum for the main skins and 5 min epoxy for leading and trailing edges, wingtip blocks, etc. I use titebond or yellow carpenter's glue to glue my wing sheeting together - solid and sands well.